Regular [Tl6]6– Cluster in Cs4Tl2O Exhibiting Closed‐Shell Configuration and Energetic Stabilization due to Relativistic Spin–Orbit Coupling

Abstract

AbstractCs4Tl2O was synthesized by reaction of the binary compounds CsTl and Cs2O at 573 K, followed by slow cooling to room temperature. According to single‐crystal X‐ray analysis, the title compound crystallizes in a new structure type (trigonal, space group R$\bar{3}$m (no. 166), a = 11.986(1), c = 20.370(2) Å, Z = 9). It consists of isolated [Tl6]6– octahedra, being regular with respect to the equality of all three main diagonals (4.546(5) Å), and of [Cs12O3]6+ triple octahedra extending along the c direction.The electronic structure of Cs4Tl2O was examined by relativistic density functional calculations including spin–orbit coupling and compared to the one of Rb10Tl6O2, which exhibits a highly distorted [Tl6]6– octahedra. In the latter case the closed‐shell electronic structure is the result of a Jahn–Teller distortion. In contrast, the regular one in Cs4Tl2O corresponds to a closed‐shell configuration, in accordance with diamagnetic properties, only if spin–orbit coupling is considered.